1. Field of the Invention
This invention relates to a vehicle headlight which is designed to switch beams between low and high beams. More particularly, the invention relates to switching beams between low and high beams by tilting a reflector vertically by a predetermined angle.
2. Description of the Related Art
Vehicle headlights are designed to emit a low or high beam by causing light from a light source bulb to be reflected forward by a reflector. With respect to light sources (discharge light-emitting portions or filaments), though different light sources are generally used for low and high beams respectively because the direction of emitting the low beam differs from that of emitting the high beam, there are also known vehicle headlights using a single light source. Particularly in such a two-lamp type vehicle headlight using a discharge bulb as a light source bulb, a single light source arrangement will have to be made often.
In the case of a vehicle headlight using such a single light source, a low beam is switched to a high beam and vice versa by mechanically displacing optical elements including a light source bulb, a reflector and the like, and a beam switching device is installed accordingly because it is reasoned to use the beam switching device for switching beams by vertically tilting the reflector by a predetermined angle. By adopting the beam switching device, the actuator of a leveling unit can also be used as the actuator of the beam switching device.
However, the following problems will arise when such a reflector-tilting type beam switching device is introduced.
As a low-beam light distribution pattern, it is preferred to use a light distribution pattern P(L) having a clear cutoff line (a light-to-shade boundary line) CL as shown in FIG. 14A in view of securing forward visibility for automobile drivers as well as preventing a glare from those driving oncoming vehicles. When an attempt is made to switch beams by vertically tilting the reflector, however, the low and high beams are to be emitted with the same light distribution pattern. Consequently, the adoption of the light distribution pattern P(L) with the cutoff line CL as a low-beam light distribution pattern will result in providing a light distribution pattern P(H) having the cutoff line CL for a low beam as shown in FIG. 14B, thus developing the problem of failing to secure upward forward visibility (the portion shown by A therein) ahead of a vehicle.